Arithmetic operation within string concatenation without parenthesis causes strange result

Question

Consider the following line of code:

The output of that is 3, which is the expec

Answer 1

Your string '10 - 7 = ' is being concatenated with $x. Then that is being interpreted as an int which results in 10 and then 7 is subtracted, resulting in 3.

For more explanation, try this:

echo (int) ('10 - 7 = ' . 10); // Prints "10"

More information on string to number conversion can be found at http://www.php.net/manual/en/language.types.string.php#language.types.string.conversion

If the string starts with valid numeric data, this will be the value used

Answer 2

In this code:

echo '10 - 7 = '.$x-$y;

The concatenation takes precedence, so what you're left with is this:

echo '10 - 7 = 10'-$y;

Because this is trying to perform integer subtraction with a string, the string is converted to an integer first, so you're left with something like this:

echo (int)'10 - 7 = 10'-$y;

The integer value of that string is 10, so the resulting arithmetic looks like this:

echo 10-$y;

Because $y is 7, and 10 - 7 = 3, the result being echoed is 3.

Answer 3

. and - have the same precedence, so PHP is reinterpreting '10 - 7 = 10' as a number, giving 10, and subtracting 7 gives 3.